Projection display apparatus 10 shown in FIG. 1 includes power source 11, ballast 12, lamp 13, image signal controller 14, display element 15, and light intensity controller 16. In FIG. 1, an outline arrow indicates a light flux.
Ballast 12 adjusts the lamp power that is supplied from power source 11 to lamp 13 for driving lamp 13, according to a power control signal input from light intensity controller 16. Lamp 13 is lit by a lamp power supplied from power source 11 via ballast 12, and illuminates display element 15.
Image signal controller 14 receives an image signal from the outside, and outputs the image signal to display element 15. Display element 15 modulates light emitted from lamp 13 according to the amplitude of the image signal input from image signal controller 14, and emits the modulated light as image light. The image light emitted from display element 15 is projected as a projection screen on screen 20.
In the case of projection in a dark room or on a small screen using the projection display apparatus as described above, in which the projection screen is excessively bright, it is sometimes difficult to see the screen.
A projection display apparatus has been discussed in which light intensity controller 16 receives a power changing operation that is input from the outside so as to change the lamp power, and changes the lamp power according to the input power changing operation.
In the case of adopting the power changing operation, when the power changing operation is input, light intensity controller 16 outputs the power control signal to ballast 12 such that the lamp power according to the power changing operation is supplied to lamp 13.
Projection display apparatus 10 described above changes the lamp power according to the power changing operation, thereby allowing the luminance of lamp 13 to be varied to adjust the brightness of the image light.
Typically, the lamp of a projection display apparatus is a discharge lamp. Accordingly, lighting at a lamp power that is lower than a predetermined power (rated power) causes unstable light emission and damages the electrode and a luminous tube of the lamp.
Thus, Patent Document 1 (JP2009-093862A) discloses a technique that, if the lamp power is lower than the rated power for a certain period of time or longer, then a lamp refreshing process is carried out to temporarily increase the lamp power to the rated power at appropriate time intervals and then returns the power to the original lamp power after elapse of a predetermined period of time. According to the technique, even if lighting lamp power so that it is lower than the rated power damages the electrode and the luminous tube of the lamp, the lamp refreshing process can return the state of the electrode and the luminous tube to the normal state.